Noncollinear spin states in TlCo_2Se_(2-x)S_x alloys from first principles

摘要

The observed transition of the magnetic structure from a noncollinear state at x=0 to a ferromagnetic phase at x=1.75, through a series of spin spirals in the substitutional TlCo_2Se_(2-x)S_x alloys, has been investigated by first principles theory. Our calculations successfully reproduced the magnetic structure of TlCo_2S_2 and the obtained magnetic moment is somewhat higher (0.82μ_β per Co atom) than the experimental value. However, TlCo_2Se_2 was found to possess an antiferromagnetic state which is inconsistent with the observed spin spiral. We show that the correct magnetic structure of TlCo_2Se_2 can be obtained if the distance between the Co layers is reduced. Moreover, we demonstrate that the modification of the Co interlayer distance is a crucial parameter that governs the nature of the magnetism in these alloys. We discuss a mechanism that could favor noncollinear states in TlCo_2Se_2 over the ferromagnetic configuration and explain the change of the magnetic structure in the substitutional TlCo_2Se_(2-x)S_x alloys.